Conventionally, authentication systems using IDs have been utilized in various fields. Among them, security systems have been widely used, for example, for preventing leakages of personal information, for controlling entrance into and exit from buildings, and for preventing forgery of documents and luxuries. That is, security systems based on advanced ID authentication are important technologies for ensuring “safety” and “security” in the 21st century society.
Examples of ID recognition methods used in conventional security systems include ID recognition methods based on material information (e.g., keys, magnetic cards, IC cards, and bar codes printed in luminescent ink), ID recognition methods based on human information (e.g., fingerprints, voice recognition, and face recognition), and ID recognition methods based on passwords (i.e., encryption of digital information).
However, these ID recognition methods have the following problems. For example, the ID recognition methods based on material information cannot completely deny the possibility of forgery or reproduction of materials. Further, the ID recognition methods based on human information reduce the precision of ID recognition due to differences in voices and faces among people. Further, information may be forged with use of a fingerprint tape, a photograph, or the like. Furthermore, the ID recognition methods based on passwords cannot completely deny the possibility of hacking since the methods use digital information.
Therefore, in order to overcome these problems, it is necessary to use technologies that perform more advanced ID recognition. Examples of such technologies include technologies using advanced-information recording materials. Further, examples of such technologies using advanced-information recording materials include technologies using light emitters. In this case, a plurality of light emitters are used for encryption. That is, an ID is authenticated in accordance with the intensity of light emitted from each of the light emitters.
Examples of the other technologies using light emitters include technologies related to identifying marks made with light emitters (such technologies being disclosed, for example, in Patent Documents 1 to 3). Patent Documents 1 to 3 disclose technologies related to identifying marks made with rare-earth complexes. Each of these patent documents uses an optically-active rare-earth complex, and checks the authenticity of an identifying mark by calculating the intensity difference between a right-handed circularly polarized component and left-handed circularly polarized component of fluorescence emitted from the optically-active rare-earth complex and by determining whether or not the intensity difference is 0.
However, the plurality of light emitters differ from one another in the rates at which the light emitters deteriorate due to light and heat and in the luminescence properties of the light emitters with respect to temperature. For this reason, the technology for measuring the intensity of light emitted from each of the light emitters and authenticating (identifying) an ID in accordance with the intensity causes variations in intensity due to differences among the light emitters in the rates at which the light emitters deteriorate and in the temperature characteristics of the light emitters. This causes errors in identification, thereby imposing restrictions on use conditions and making long-term use difficult.
Further, each of the technologies described in the foregoing patent documents checks the authenticity of an identifying mark simply by measuring the presence or absence of circularly-polarized light. For this reason, the technologies can be used for preventing forgery of pieces of paper money and securities. However, the technologies are inappropriate for identification and authentication of identification information such as IDs for the following reasons: (1) There are scarcities in types of optically-anisotropic complex; (2) It is more difficult to purify an optically-anisotropic complex than to purify a normal complex; and (3) An optically-anisotropic complex is at least 2000 times as expensive as a rare-earth complex that is not optically active.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 111704/2005 (Tokukai 2005-111704; published on Apr. 28, 2005)    Patent Document 2: Japanese Unexamined Patent Application Publication No. 112947/2005 (Tokukai 2005-112947; published on Apr. 28, 2005)    Patent Document 3: Japanese Unexamined Patent Application Publication No. 114909/2005 (Tokukai 2005-114909; published on Apr. 28, 2005)